The present invention relates to a coating installation and method of operating the same, and, more particularly, to an electrostatic powder coating installation which includes a cabinet or housing accommodating a means for discharging electrostatically charged powder, a filter strip, located at a floor or base of an inner space of the cabinet and being capable of being moved or displaced through the cabinet, a first suction fan, having a large surface area, installed in an area of the bottom of the cabinet for generating a suction field with a vacuum in the cabinet through the filter strip, cleaning means associated with the filter strip for removing surplus powder lying on the filter strip, and a powder recovery means for the electrostatic powder coating installation which includes a sifting machine, a basket for sifting material, a dirt- or contaminant-catching container, a filtering device, a fan, and a floor or base member which is at least partially fluidizing and a powder drawing element.
In, for example, European Pat. No. 0 141 778, a suction system for powdered material, especially powder coating chambers with at least one movable suction nozzle and at least one suction air duct functionally connected with the suction nozzle, is proposed, with the duct having a suction fan or blower, and with the powder coating chamber being provided with a bottom filter and a movable suction nozzle, bottom pan, and suction blower or fan whereby it is possible to carry sprayed powder by a shortest route back to a dispensing container.
A disadvantage of this proposed system resides in the fact that certain problems develop in the coating chamber with regard to a transition from the longitudinally displaceable nozzle to the suction system.
More particularly, in the proposed suction system of the above-noted European patent application, in the coating chamber, the filter belt is stationary during a coating process, with a nozzle traveling back and forth over an entire length of the belt, and with the falling powder being collected through slots. Since a connection of the nozzle to the exterior is accomplished by a hose, the hose is always in a vicinity of the coating operation thereby creating considerable problems.
In, for example, Auslegeschrift No. 2,546,920 and U.S. Pat. No. 4,245,551, an apparatus of the aforementioned type, arranged in the cabinet or housing, is proposed; however, one of the biggest problems or disadvantages of the proposed apparatus resides in the fact that the proposed systems are complex and too much time is lost when the pigment is changed.
More particularly, in the installation described in U.S. Pat. No. 4,245,551, it is necessary to replace the entire filter unit when the pigment changes. However, the filters are relatively expensive and, the system is relatively large therefore a considerable amount of space is required for each pigment. In this connection, replacing a filter unit, normally in the form of pocket filters or cartridge filters is difficult and, with this proposed system, one structural unit is always required for each pigment.
In the aforementioned Auslegeschrift, it is necessary to replace the filter strips for each pigment and generally at least two people are required to change the strips. Furthermore, the filter strips have to be stored separately and, in many cases, the situation arises that two or more suction units must be provided to minimize the time consumed in changing the pigment.
Swiss Application No. 4,904/83-2 also provides an example of an electrostatic powder coating apparatus; however, as with the above-noted United States patent and the Auslegeschrift, the apparatus and associated process are relatively complicated and require substantial investment to manufacture the apparatus all of which constitute obstacles to a widespread use of an electrostatic powder coating apparatus. Moreover, in the proposed apparatus the suction removal, sifting and returning of the powder is very elaborate and very expensive.
The same complex problems arise in a direct removal of the powder by suction in a coating procedure for special uses such as, for example, in coating the seams of cans. In the systems which have been proposed, the powder, removed by suction, is precipitated from the air in a filter and falls on a floor or base of the filter housing and, from there, the powder is conveyed to a sifting machine either by an intermediate conveying device through a mini-cyclone separator and a bucket wheel sluiceway or squeeze valve. From there the cleaned powder is directly forwarded to the powder container.
The aim underlying the present invention essentially resides in providing a multipigment electrostatic coating installation and method of operating the same which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
In accordance with advantageous features of the present invention, an electrostatic powder coating installation is provided which includes a means for pulling or drawing a filter strip for at least one length of the cabinet or housing of the installation when the pigment changes thereby assigning a filter strip zone to every pigment.
In accordance with still further features of the present invention, to achieve a significant structural simplification, elements generally employed in the prior art installations especially elements which tend to break down are eliminated. More particularly, bucket wheel sluiceways which tend to get jammed when loaded with powder or squeezing valves which have a high rate of wear and tear on the rubber and cause the powder to cake so as to prevent satisfactory operation need not be provided nor is it necessary to provide an intermediate conveying apparatus which requires additional compressed air and associated components which are also susceptible to wear and tear.
In accordance with the present invention, the recovery apparatus of the electrostatic powder coating installation includes a direct powder feed pipe leading to a sifting machine. Moreover, the basket for sifting material and the filtering apparatus are disposed in the same enclosed space and, by virtue of such location, a means are provided for transporting powder away to carry the powder which is sifted out by the sifting machine and the powder which falls on the filtering apparatus so that the powder can be used again with the entire structural unit being replaceable as a module.
Advantageously, in accordance with the present invention, a suction nozzle is provided which includes a propulsion adapted to move the suction nozzle along the filter strip. The suction system of the present invention is adapted to operate intermittently and a fibrous web, preferably one that can be rolled and unrolled is disposed beneath the filter strip.
According to the present invention, the suction system for powdered material, especially for a powder coating chamber of an electrostatic powder coating installation, includes at least one movable suction nozzle and at least one suction air duct, with a suction fan or blower being functionally connected with the at least one suction nozzle. The at least one suction nozzle is functionally connected with at least one drive belt for moving the at least one nozzle with respect to an air suction channel, which channel is open along one longitudinal side thereof and sealed by the drive belt.
The powder coating chamber of the present invention includes a bottom filter and a movable suction nozzle, bottom pan, and suction fan or blower, with the suction nozzle being moved back and forth by a belt and drive motor arrangement, and with the belt simultaneously serving as a sealing element for a slot of an air suction exhaust duct.
Advantageously, the belt is interrupted and fastened to transverse guide frame means whereby the powder-air stream can pass through the nozzle and through a section in a guide frame in each position into the longitudinally air suction exhaust duct.
The nozzle, in accordance with the present invention, may be inserted in a guide frame and include one or more elements sealed against one another by resilient or rubber lip members.
The longitudinally extending air suction exhaust duct may include a section which is provided over an entire belt length with a longitudinal slot and sealed at the ends with removable cover means for facilitating a cleaning. The belt may, for example, take the form of a toothed belt.
It is also possible in accordance with the present invention for a slotted duct to be provided on each side of the chamber and optionally provided nozzle elements installed so that suction can be shifted alternately depending upon the color of the powdered material from one side to the other in the longitudinal duct.
The longitudinally extending air suction exhaust duct, in addition to a return connection, has at least one additional connection which is adapted to connect a suction hose when cleaning the coating chamber. To facilitate a driving of the drive motor, an appropriate slip clutch may be provided in the belt drive system.
Preferably, in accordance with still further features of the present invention, an entrance feed pipe into the sifting machine is arranged tangentially and an air suction device is located at one end of the sifting machine to generate a potential sump in the machine.
The longitudinal axis of the sifting machine may, in accordance with the present invention, be inclined in a direction of the container for catching dirt or contaminants and the apparatus may be arranged in such a manner that a cleaning by filtering can take place right in the filtering space of the shifting machine individually or in blocks thereby making a continuous operation possible.
At least a floor or base member of the filtering space of the sifting machine is made of porous material and, preferably, the floor or base is inclined.
Advantageously, the individual units of the powder coating installation and, for example, the powder container are replaceable and, preferably, without the use of any specialized tools.
In accordance with the method of electrostatic powder coating of the invention, during a spraying, the filter strip is moved only when the pigment changes to get a portion of the filter strip associated with the new pigment ready inside the cabinet or housing. Moreover, the suction nozzle of the electrostatic powder coating installation is preferably operated intermittently.
The contaminant- or dirt-catching container of the electrostatic powder coating installation of the present invention is advantageously maintained at the same pressure level as an area containing the filter and sifting machine is sealed off.
Accordingly, it is an object of the present invention to provide an electrostatic powder coating installation, powder recovery installation for the electrostatic powder coating installation, and a method for operating the electrostatic powder coating installation which is simple in construction and therefore relatively inexpensive to manufacture.
A further object of the present invention resides in providing an electrostatic powder coating installation, powder recovery installation for the electrostatic powder coating installation and a method for operating the installation which is relatively small and which dispenses with the need for various conventional elements while nevertheless achieving the same separation characteristics and degree of effectiveness.
A still further object of the present invention resides in providing an electrostatic powder coating installation and a powder recovery installation for the electrostatic powder coating installation which functions reliably under all operating conditions.
Yet another object of the present invention resides in providing a suction system for powdered material, especially for powder coating chambers of electrostatic powder coating installations which enables the provision of an air path for suction and cleaning and which simplifies color changing in the coating installation. Another object of the present invention resides in providing a powder coating chamber which includes a displaceable suction nozzle movable back and forth by a belt and drive motor, with the belt simultaneously serving as a sealing element for a slot of an air suction exhaust air duct.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, several embodiments in accordance with the present invention.